The previous fifty years of study on the inductive events that surround early kidney development have focused on the two major cell types, the mesenchyme and epithelium. Recent work in other organs, such as liver and pancreas, have indicated a role for vascular cells in early organ development [6, 7], In this grant we present our recent results demonstrating a role for vascular cells in early kidney development. A population of Flk-1-expressing angioblasts appears to be crucial in maintaining mesenchymal condensates at a level of competence that is required for the ureteric bud to induce the mesenchymal to epithelial conversion that results in the formation of nephrons. Our present results, obtained using a novel system for microinjecting and electroporating embryonic kidney organ cultures, demonstrates that Wt1 is able to induce expression of vascular endothelial growth factor (VEGF-A). Thus, our current model suggests that Wt1 induces expression of VEGF to stimulate the angioblast population, which in turn provides an as yet unidentified signal that acts on the mesenchyme to stimulate expression of GDNF and maintain branching morphogenesis. The aims of this grant are designed to more fully determine the molecular nature of the angioblast signal, and how it may be involved in stimulating branching, and patterning the embryonic kidney.